1. Field of the Invention
This invention relates to a video signal processing apparatus for processing video signals.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows in outline the arrangement of the conventional video tape recorder as a video signal processing apparatus. The illustration includes a magnetic tape 1 which is employed as a recording medium, a rotary drum 2, a magnetic head 3 which is mounted on the rotary drum 2, a signal processing circuit 4 arranged to process signals reproduced by the magnetic head 3, a change-over switch 5 arranged to switch the signals outputted from the signal processing circuit 4, a system control circuit 6, an input terminal 8 for receiving an input signal from an external apparatus or the like, an output terminal 9, a display part 10, and an operation part 11 which is provided for instructing the apparatus to perform actions as desired.
With the video tape recorder arranged in this manner, when the operation part 11 is operated to select a reproduction mode, the system control circuit 6 controls the change-over switch 5 to allow a signal reproduced from the magnetic tape 1 to be supplied from the output terminal 9 to the display part (or monitor) 10. In the event of an operation mode other than the reproduction mode, the change-over switch 5 is controlled to allow a signal received from an external apparatus to be supplied via the input terminal 8 to the display part 10. In the case of the reproduction mode, a video signal outputted from the change-over switch 5 is supplied to the display part 10 to have a video image displayed there according to the video signal.
The video tape recorder of the above-stated kind is generally provided with an equalizer circuit for the purpose of correcting the frequency characteristic of a video signal reproduced from the magnetic tape. The equalizer circuit is arranged to correct a frequency characteristic peculiar to the magnetic tape. Reproduced video images can be adequately displayed by virtue of the correcting action of the equalizer circuit. The amount of the frequency characteristic correction by the equalizer is normally predetermined at a fixed value.
Further, in the video tape recorder, the magnetic tape is wrapped more than a half circle around the rotary drum. An information signal such as a video signal is recorded or the record of the information signal is reproduced on or from the magnetic tape by means of the magnetic head which is mounted on the periphery of the rotary drum. The information signal cannot be adequately recorded or reproduced if the magnetic head is not correctly adjusted. Generally, therefore, the magnetic head is variously adjusted at the time of manufacture, etc. The magnetic head adjusting work is done by using a testing magnetic tape and a testing magnetic head.
Further, by specifying the characteristic of the magnetic tape employed as a recording medium, the frequency characteristic of a signal processing action to be carried out at the time of recording and the recording characteristic of the magnetic head, it is practiced to arrange the equalizer circuit to have a predetermined frequency characteristic for correcting into an optimum state a reproduced signal obtained from the magnetic tape at the time of reproduction, and to demodulate the reproduced signal after the frequency characteristic of the signal is corrected by the equalizer circuit.
The conventional video tape recorder is further provided with a noise reduction circuit for lessening a noise component mixed in a video signal reproduced from the magnetic tape. The S/N ratio of the reproduced video signal can be improved by the noise reduction circuit. However, the amount of noise reduction by the noise reduction circuit is fixed and is not variable according to the S/N ratio of the reproduced video signal.
Meanwhile, with the conventional video tape recorder arranged in the above-stated manner as a video signal processing apparatus, for example, as shown in FIG. 1, no signal is obtained from the output terminal 9 in cases where the input terminal 8 has no input signal from an external apparatus or where an instruction for a mode other than the reproduction mode, such as a magnetic tape fast feeding mode or a magnetic tape rewinding mode is given. In such a case, therefore, a video image displayed at the display part 10 teems with noises, which make the video image display highly disagreeable.
Further, in correcting the frequency characteristic of a reproduced video signal by means of the equalizer circuit, unevenness in performance among the magnetic heads causes inconstancy in the frequency characteristic of the reproduced video signal as the amount of correction by the equalizer circuit is fixed to a preset value. As a result, the picture quality of the reproduced video image obtainable on the display part 10 by one video tape recorder varies from the picture quality obtainable by another video tape recorder. Even if the unevenness of the magnetic heads is adjusted at the time of manufacture, the repeated use of the video tape recorder and the secular change such as the wear of the magnetic head, etc., cause some change in the frequency characteristic of the magnetic head, thereby preventing adequate recording and reproduction of video signals.
Further, the unevenness of characteristics among the magnetic heads and the recording media such as magnetic tapes results in variations of the frequency characteristics of signals reproduced from the recording media by different video signal processing apparatuses. Therefore, the use of an equalizer circuit having a single fixed frequency characteristic is apt to be incapable of adequately correcting the frequency characteristic at the time of reproduction. The reproduction characteristic of one video signal processing apparatus thus becomes different from that of another video signal processing apparatus.
Further, as mentioned above, the noise reducible amount by the noise reduction circuit is fixed to a preset value. Therefore, while the reproduced video signal can be improved in S/N ratio, the resolution of details of the picture pattern of the reproduced video image is degraded. It is thus impossible to adjust the picture quality according to the picture pattern of the reproduced video image. Further, the S/N ratio of a reproduced video signal to be outputted from the apparatus is determined by the S/N ratio of the signal reproduced by the magnetic head. It is, therefore, impossible to process the reproduced video signal appositely to the state of the signal for a more agreeable display of the reproduced video image.